A popular theory of this year's midterm election holds that Democrats took a shellacking in part because big chunks of the party's core liberal base, discouraged at the path of the Obama administration, stayed home rather than show up to vote as they did in 2008.

It's an interesting narrative. It also doesn't appear to be entirely accurate.

While it's correct that some key parts of the Democratic coalition—young voters and African-Americans among them—didn't perform as they did in 2008, evidence emerging as the dust settles from this month's election suggests the bigger hole in the side of the Democratic ship came from moderates in the political center who didn't show up. (Those absences were in addition to the wave of independent swing voters also from the center who, exit polls showed, turned out but switched their votes to the Republicans.)

The case of the missing voters is important because how it is resolved will go a long way toward determining how Democrats respond to their midterm woes. If they conclude, as some argue, that the problem was an undermotivated liberal base, then the logical reaction would be a turn to the left and a staunch resistance to compromises with the Republicans who now control the House and hold expanded power in the Senate.